Sorting a Matrix based on a identified vector.

i would like to sort the following 4x4 matrix in an order as shown below:

for u=1:4
  Block=randi([0,1],1,4);
  Random(Rand1(u),:)=Block;
  RandSorted(A(u),:)=???;
end

where Rand1=[3 2 4 1] and A=[1 2 3 4];,

i would like to resort it back to A instead of Rand1. thank you,

[Jan]

I do not understand, what you want to achieve. While A(u) has the same value as u, what is the purpose of A?

Answer 1

[Arjun]

Hi @Mohannad Alzard,

I understand that there is an array containing binary entries which is shuffled according to the order specified by vector “Rand1” and now you want to reorder the rows as per order specified by vector “A”.

To reorder the matrix back to the order specified by the vector A, you need to rearrange the rows that were initially shuffled using Rand1. The key operation is:

“RandSorted(A(u), :) = Random(Rand1 == A(u), :)” where “RandSorted” is the final answer matrix.

Below is the explanation of the above condition:

• A(u) gives the target position in the original order. For example, when u is 1, A(1) is 1, indicating that the first row in “RandSorted” should be filled.
• Rand1 == A(u) finds the position in Rand1 that corresponds to the current original order position A(u).
• Random(Rand1 == A(u), :) selects the row from Random that was initially at position A(u) before it was shuffled. This uses logical indexing to find the correct row.
• RandSorted(A(u), :) = ... assigns the selected row from Random to the correct position in “RandSorted”, effectively reversing the shuffle.

Kindly refer to the code below to have a better understanding:

% Initialization 
Rand1 = [3 2 4 1]; 
A = [1 2 3 4]; 
Random = zeros(4, 4); 
% Generate the random matrix and shuffle according to Rand1 
for u = 1:4 
    Block = randi([0, 1], 1, 4); 
    Random(Rand1(u), :) = Block; 
end 
% Initialize the answer matrix 
RandSorted = zeros(4, 4); 
% Sort the matrix back to the order specified by A 
for u = 1:4 
    RandSorted(A(u), :) = Random(Rand1 == A(u), :); 
end 
% Display the sorted matrix 
disp(RandSorted); 

I hope this will help!